The University of Chicago Comprehensive Cancer Center (UCCCC) Transgenic Mouse/Embryonic Stem Cell Facility provides comprehensive genetic engineering services to alter the genome of the laboratory mouse. The UCCCC has many invesfigators who use mouse models as their primary tool of analysis, as well as a multitude of addifional investigators who require the occasional mouse model in their studies of the causes and treatment of cancer. The generation and maintenance of transgenic animals through the microinjection of single-celled mouse embryos, and the generation of genetically modified mice through the use of ES cells require specialized technical personnel. Furthermore, such efforts necessitate the acquisition of an array of devoted equipment. Thus, the availability of a shared resource greatly reduces research costs for the individual investigators of the UCCCC. The existence of this Facility also greatly increases the accessibility of genetic engineering technology to investigators with limited related experience. The UCCCC Transgenic Mouse/Embryonic Stem Cell Facility was established in 1991, and has been tremendously productive and successful; the range of services provided has expanded considerably since it's founding. Services provided by the Transgenic Mouse/Embryonic Stem Cell Facility include: 1) transgenic mouse production from founder through F1 Stage; 2) ES cell technology mouse production; 3) ES cell gene targeting and culturing; 4) embryo rederivation; 5) mouse embryonic feeder (MEF) cell production; 6) Timed pregnancies of various strains and lines of mice; 7); various breeding services and GEM model line maintenance; 8) DNA preparation from ES cell lines; and 9) design and construction of transgenic or ES cell targeting vectors. In addition to the technical services, the Facility also offers assistance with the design of studies that require mouse molecular genetics, as well as advice and instruction on mouse handling and breeding. In providing these comprehensive services, the UCCCC Transgenic Mouse/Embryonic Stem Cell Facility has generated mouse models that have led to advances in our understanding of cancer, including cancers of the breast, skin, colon, brain and prostate.